ANSI S1.4: Electroacoustics — Sound Level Meters

American national standard for sound level meters, specifying Type 0, 1, and 2 instrument requirements.

ANSI S1.4: American National Standard for Sound Level Meters

ANSI S1.4 (and its current revision ANSI/ASA S1.4-2014) is the United States national standard for sound level meters (SLMs). It defines the performance requirements, tolerance limits, and testing procedures for instruments used to measure sound pressure levels. This standard is the primary reference for noise measurement equipment used in OSHA compliance, environmental monitoring, and acoustic consulting in the US.

Type Classifications

ANSI S1.4 defines three accuracy classes. Type 0 (laboratory reference) instruments have the tightest tolerances and are used as calibration references. Type 1 (precision) meters are suitable for field measurements where high accuracy is required, such as regulatory compliance and engineering studies. Type 2 (general purpose) meters have wider tolerances and are acceptable for general noise surveys and screening measurements. The differences between types primarily relate to the allowable frequency response deviation, directional response, and environmental sensitivity.

Relationship to IEC 61672

The international equivalent is IEC 61672-1, which defines Class 1 and Class 2 sound level meters. ANSI S1.4 Type 1 corresponds approximately to IEC 61672 Class 1, and Type 2 corresponds to Class 2. Modern instruments are typically designed to meet both standards simultaneously. IEC 61672 has largely superseded ANSI S1.4 in international markets, but ANSI S1.4 remains the reference standard cited by OSHA and many US regulatory agencies.

Key Requirements

The standard specifies A, C, and Z (flat) frequency weightings, along with Fast (125 ms), Slow (1000 ms), and Impulse (35 ms attack, 1500 ms decay) time weightings. It defines the reference direction, frequency range (20 Hz to 20 kHz minimum), dynamic range, and overload indicators. Periodic calibration with a reference source (typically 94 dB at 1 kHz) is required before each measurement session.

SonaVyx Compliance

SonaVyx's SPL meter implements all frequency and time weightings specified by ANSI S1.4 with IEC 61672-1 Class 2 tolerance targets. The calibration system allows users to calibrate against a known reference source to compensate for microphone sensitivity variations.